Electroluminescent devices

ABSTRACT

An electroluminescent device has, as the electroluminescent layer, a metal compound selected from organic complexes of non rare earth metals.

[0001] The present invention relates to electroluminescent devices.

[0002] Materials which emit light when an electric current is passedthrough them are well known and used in a wide range of displayapplications. Liquid crystal devices and devices which are based oninorganic semiconductor systems are widely used, however these sufferfrom the disadvantages of high energy consumption, high cost ofmanufacture, low quantum efficiency and the inability to make flat paneldisplays.

[0003] Organic polymers have been proposed as useful inelectroluminescent devices, but it is not possible to obtain purecolours, they are expensive to make and have a relatively lowefficiency.

[0004] Another compound which has been proposed is aluminium quinolate,but this requires dopants to be used to obtain a range of colours andhas a relatively low efficiency.

[0005] Patent application WO98/58037 describes a range of lanthanidecomplexes which can be used in electroluminescent devices which haveimproved properties and give better results. Patent ApplicationsPCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024,PCT/GB99/04028, PCT/GB00/00268 describe electroluminescent complexes,structures and devices using rare earth chelates.

[0006] Apart from aluminium quinolate which is a poor electroluminescentcompound all electroluminescent compounds have been based on rareearths, lanthanide and actinide complexes.

[0007] We have now devised improved electroluminescent devices andstructures using a non rare earth complex.

[0008] According to the invention there is provided anelectroluminescent structure comprising (i) a first electrode and (ii)an electroluminescent layer comprising a layer of a light emitting metalcompound selected from organic complexes of non rare earth metals and(iii) a second electrode.

[0009] The invention also provides an electroluminescent devicecomprising (i) a first electrode, (ii) a layer of a hole transmittingmaterial (iii) an electroluminescent layer comprising a layer of a lightemitting metal compound selected from organic complexes of non rareearth metals and (iv) a second electrode.

[0010] The complexes have the formula (M) (Lα)_(n) where M is the metaland n is the valency state of the metal.

[0011] The light emitting metal compound can be formed from any metalcompound selected from non rare earth metals e.g. lithium, sodium,potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium,barium, copper, silver, gold, zinc, cadmium, boron, aluminium, gallium,indium, germanium, tin, antimony, lead, and metals of the first, secondand third groups of transition metals e.g. manganese, iron, ruthenium,osmium, cobalt, nickel, palladium, platinum, cadmium, chromium.titanium, vanadium, zirconium, tantulum, molybdenum, rhodium, iridium,titanium, niobium, scandium, yttrium etc. which emit light when anelectric current is passed through it.

[0012] Preferably Lα is selected from β diketones such as those offormulae

[0013] where R₁, R₂ and R₃ can be the same or different and are selectedfrom hydrogen, and substituted and unsubstituted hydrocarbyl groups suchas substituted and unsubstituted aliphatic groups, substituted andunsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorocarbons such as trifluoryl methyl groups, halogens such asfluorine or thiophenyl groups; R₁, R₂ and R₃ can also form substitutedand unsubstituted fused aromatic, heterocyclic and polycyclic ringstructures and can be copolymerisable with a monomer e.g. styrene. X isSe, S or O, Y can be hydrogen, substituted or unsubstituted hydrocarbylgroups, such as substituted and unsubstituted aromatic, heterocyclic andpolycyclic ring structures, fluorine, fluorocarbons such as trifluorylmethyl groups, halogens such as fluorine or thiophenyl groups ornitrile.

[0014] Examples of R₁ and/or R₂ and/or R₃ include aliphatic, aromaticand heterocyclic alkoxy, aryloxy and carboxy groups, substituted andsubstituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene,naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclicgroups such as carbazole.

[0015] Some of the different groups Lα may also be the same or differentcharged groups such as carboxylate groups so that the group L₁ can be asdefined above and the groups L₂, L_(3 . . .) can be charged groups suchas

[0016] where R is R₁ as defined above or the groups L₁, L₂ can be asdefined above and L_(3 . . .) etc. are other charged groups.

[0017] R₁, R₂ and R₃ can also be

[0018] where X is O, S, Se or NH.

[0019] A preferred moiety R₁ is trifluoromethyl CF₃ and examples of suchdiketones are, banzoyltrifluoroacetone, p-chlorobenzoyltrifluoroacetone,p-bromotrifluoroacetone, p-phenyltrifluoroacetone,1-naphthoyltrifluoroacetone, 2-naphthoyltrifluoroacetone,2-phenathoyltrifluoroacetone, 3-phenanthoyltrifluoroacetone,9-anthroyltrifluoroacetonetrifluoroacetone, cinnarnoyltrifluoroacetone,and 2-thenoyltrifluoroacetone.

[0020] The different groups Lα may be the same or different ligands offormulae

[0021] where X is O, S, or Se and R₁ R₂ and R₃ are as above

[0022] The different groups Lα may be the same or different quinolatederivatives such as

[0023] where R is hydrocarbyl, aliphatic, aromatic or heterocycliccarboxy, aryloxy, hydroxy or alkoxy e.g. the 8 hydroxy quinolatederivatives or

[0024] where R, R₁, and R₂ are as above or are H or F e.g. R₁ and R₂ arealkyl or alkoxy groups

[0025] As stated above the different groups Lα may also be the same ordifferent carboxylate groups e.g.

[0026] where R₅ is a substituted or unsubstituted aromatic, polycyclicor heterocyclic ring a polypyridyl group, R₅ can also be a 2-ethyl hexylgroup so L_(n) is 2-ethylhexanoate or R₅ can be a chair structure sothat L_(n) is 2-acetyl cyclohexanoate or Lα can be

[0027] where R is as above e.g. alkyl, allenyl, amino or a fused ringsuch as a cyclic or polycyclic ring.

[0028] The different groups Lα may also be

[0029] Where R, R₁ and R₂ are as above.

[0030] Examples of β-diketones are Tris-(1,3-diphenyl-1-3-propanedione)(DBM) and suitable metal complexes are Al(DBM)₃, Zn(DBM)₂ and Mg(DBM)₂,Sc(DBM)₃ etc.

[0031] A preferred β-diketone is when R₁ and/or R₃ are alkoxy such asmethoxy and the metals are aluminium or scandium i.e. the complexes havethe formula

[0032] where R₄ is an alkyl group, preferably methyl and R₃ is hydrogen,an alkyl group such as methyl or R₄O.

[0033] There can be other ligands in place of some of the β-diketonecomplex such as

[0034] so that the electroluminescent compound has the formula(Lα)_(m)(L₁)_(n)M where M is as defined above, (Lα) is a compound offormula

[0035] where R₁, R₂, and R₃ are as defined above, L₂ is another organicligand, m+n equals the valency of M and m is at least 1.

[0036] When M is platinum or palladium the complex can benon-stoichiometric i.e. of formula M_(x)L_(y) where M is the metal and Lis an organic ligand. In a stoichiometric complex x will be one and ywill be the valence state of the metal, in a non-stoichiometric complexx and y can have different values e.g. x is two and y is three, examplesinclude Pt₂(DBM)₃ and Pd₂(DBM)₃ where Pt and Pd are nominally in the IIvalence state. It is possible that some kind of linked or polymericstructure is formed and/or the metal is present in more than one valencestate.

[0037] Where the metal M is a metal with an unfilled inner orbital suchas scandium, yttrium, niobium etc. there can be an uncharged ligandwhich forms a complex with the metal so the complex has the formula

[0038] where M is as a metal with an unfilled inner orbital Lα is asabove

[0039] The groups L_(P) can be selected from

[0040] Where each Ph which can be the same or different and can be aphenyl (OPNP) or a substituted phenyl group, other substituted orunsubstituted aromatic group, a substituted or unsubstitutedheterocyclic or polycyclic group, a substituted or unsubstituted fusedaromatic group such as a naphthyl, anthracene, phenanthrene or pyrenegroup. The substituents can be for example an alkyl, aralkyl, alkoxy,aromatic, heterocyclic, polycyclic group, halogen such as fluorine,cyano, amino. Substituted amino etc. Examples are given in FIGS. 1 and 2of the drawings where R, R₁, R₂, R₃ and R₄ can be the same or differentand are selected from hydrogen, hydrocarbyl groups, substituted andunsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorocarbons such as trifluoryl methyl groups, halogens such asfluorine or thiophenyl groups; R, R₁, R₂, R₃ and R₄ can also formsubstituted and unsubstituted fused aromatic, heterocyclic andpolycyclic ring structures and can be copolymerisable with a monomere.g. styrene. R, R₁, R₂, R₃ and R₄ can also be unsaturated alkylenegroups such as vinyl groups or groups

—C—CH₂═CH₂—R

[0041] where R is as above.

[0042] L_(p) can also be compounds of formulae

[0043] where R₁, R₂ and R₃ are as referred to above, for examplebathophen shown in FIG. 3 of the drawings in which R is as above or

[0044] where R₁, R₂ and R₃ are as referred to above.

[0045] L_(p) can also be

[0046] where Ph is as above.

[0047] Other examples of L_(p) chelates are as shown in FIG. 4 andfluorene and fluorene derivatives e.g. a shown in FIG. 5 and compoundsof formulae as shown as shown in FIGS. 6 to 8.

[0048] Specific examples of Lα and Lp are tripyridyl and TMHD, and TMHDcomplexes, α, α′, α″ tripyridyl, crown ethers, cyclans, cryptansphthalocyanans, porphoryins ethylene diamine tetramine (EDTA), DCTA,DTPA and TTHA. Where TMHD is 2,2,6,6-tetramethyl-3,5-heptanedionato andOPNP is diphenylphosphonimide triphenyl phosphorane. The formulae of thepolyamines are shown in FIG. 9.

[0049] Preferably there is a hole transmitting layer deposited on thetransparent substrate and the electroluminescent material is depositedon the hole transmitting layer. The hole transmitting layer serves totransport holes and to block the electrons, thus preventing electronsfrom moving into the electrode without recombining with holes. Therecombination of carriers therefore mainly takes place in the emitterlayer.

[0050] Hole transmitting layers are used in small molecule based polymerelectroluminescent devices and in electroluminescent devices based onrare earth metal complexes and any of the known hole transmittingmaterials in film form can be used.

[0051] Hole transmitting layers are used in polymer electroluminescentdevices and any of the known hole transmitting materials in film formcan be used.

[0052] The hole transmitting layer can be made of a film of an aromaticamine complex such as poly (vinylcarbazole),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD),an unsubstituted or substituted polymer of an amino substituted aromaticcompound, a polyaniline, substituted polyanilines, polythiophenes,substituted polythiophenes, polysilanes etc. Examples of polyanilinesare polymers of

[0053] where R is in the ortho- or meta-position and is hydrogen, C1-18alkyl, C1-6 alkoxy, amino, chloro, bromo, hydroxy or the group

[0054] where R is alky or aryl and R′ is hydrogen, C1-6 alkyl or arylwith at least one other monomer of formula I above.

[0055] Polyanilines which can be used in the present invention have thegeneral formula

[0056] where p is from 1 to 10 and n is from 1 to 20, R is as definedabove and X is an anion, preferably selected from Cl, Br, SO₄, BF₄, PF₆,H₂PO₃, H₂PO₄, arylsulphonate, arenedicarboxylate, polystyrenesulphonate,polyacrylate alkysulphonate, vinylsulphonate, vinylbenzene sulphonate,cellulosesulphonate, camphor sulphonates, cellulose sulphate or aperfluorinated polyanion.

[0057] Examples of arylsulphonates are p-toluenesulphonate,benzenesulphonate, 9,10-anthraquinone-sulphonate andanthracenesulphonate, an example of an arenedicarboxylate is phthalateand an example of arenecarboxylate is benzoate.

[0058] We have found that protonated polymers of the unsubstituted orsubstituted polymer of an amino substituted aromatic compound such as apolyaniline are difficult to evaporate or cannot be evaporated, howeverwe have surprisingly found that if the unsubstituted or substitutedpolymer of an amino substituted aromatic compound is de-protonated itcan be easily evaporated i.e. the polymer is evaporable.

[0059] Preferably evaporable de-protonated polymers of unsubstituted orsubstituted polymer of an amino substituted aromatic compound are used.The de-protonated unsubstituted or substituted polymer of an aminosubstituted aromatic compound can be formed by deprotonating the polymerby treatment with an alkali such as ammonium hydroxide or an alkalimetal hydroxide such as sodium hydroxide or potassium hydroxide.

[0060] The degree of protonation can be controlled by forming aprotonated polyaniline and de-protonating. Methods of preparingpolyanilines are described in the article by A. G. MacDiarmid and A. F.Epstein, Faraday Discussions, Chem Soc.88 P319 1989.

[0061] The conductivity of the polyaniline is dependant on the degree ofprotonation with the maximum conductivity being when the degree ofprotonation is between 40 and 60% e.g. about 50% for example.

[0062] Preferably the polymer is substantially fully de-protonated

[0063] A polyaniline can be formed of octamer units i.e. p is four e.g.

[0064] The polyanilines can have conductivities of the order of 1×10⁻¹Siemen cm⁻¹ or higher.

[0065] The aromatic rings can be unsubstituted or substituted e.g. by aC1 to 20 alkyl group such as ethyl.

[0066] The polyaniline can be a copolymer of aniline and preferredcopolymers are the copolymers of aniline with o-anisidine, m-sulphanilicacid or o-aminophenol, or o-toluidine with o-aminophenol,o-ethylaniline, o-phenylene diamine or with amino anthracenes.

[0067] Other polymers of an amino substituted aromatic compound whichcan be used include substituted or unsubstituted polyaminonapthalenes,polyaminoanthracenes, polyaminophenanthrenes, etc. and polymers of anyother condensed polyaromatic compound. Polyaminoanthracenes and methodsof making them are disclosed in U.S. Pat. No. 6,153,726. The aromaticrings can be unsubstituted or substituted e.g. by a group R as definedabove.

[0068] The polyanilines can be deposited on the first electrode byconventional methods e.g. by vacuum evaporation, spin coating, chemicaldeposition, direct electrodeposition etc. preferably the thickness ofthe polyaniline layer is such that the layer is conductive andtransparent and can is preferably from 20 nm to 200 nm. The ployanilinescan be doped or undoped, when they are doped they can be dissolved in asolvent and deposited as a film, when they are undoped they are solidsand can be deposited by vacuum evaporation i.e. by sublimation.

[0069] The structural formulae of some other hole transmitting materialsare shown in FIGS. 11, 12, 13 and 14 of the drawings, where R, R₁, R₂and R₃ can be the same or different and are selected from hydrogen, andsubstituted and unsubstituted hydrocarbyl groups such as substituted andunsubstituted aliphatic groups, substituted and unsubstituted aromatic,heterocyclic and polycyclic ring structures, fluorocarbons such astrifluoryl methyl groups, halogens such as fluorine or thiophenylgroups; R₁, R₂ and R₃ can also form substituted and unsubstituted fusedaromatic, heterocyclic and polycyclic ring structures and can becopolymerisable with a monomer e.g. styrene. X is Se, S or O, Y can behydrogen, substituted or unsubstituted hydrocarbyl groups, such assubstituted and unsubstituted aromatic, heterocyclic and polycyclic ringstructures, fluorine, fluorocarbons such as trifluoryl methyl groups,halogens such as fluorine or thiophenyl groups or nitrile.

[0070] Examples of R₁ and/or R₂ and/or R₃ include aliphatic, aromaticand heterocyclic alkoxy, aryloxy and carboxy groups, substituted andsubstituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene,naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclicgroups such as carbazole.

[0071] The hole transporting material can optionally be mixed with theelectroluminescent material in a ratio of 5-95% of theelectroluminescent material to 95 to 5% of the hole transportingcompound.

[0072] Other hole transporting materials which can be used areconjugated polymers.

[0073] U.S. Pat. No. 5,807,627 discloses an electroluminescence devicein which there are conjugated polymers in the electroluminescent layer.The conjugated polymers referred to are defined as polymers for whichthe main chain is either fully conjugated possessing extended pimolecular orbitals along the length of the chain or else issubstantially conjugated, but with interruptions to conjugation, eitherrandom or regular along the main chain. They can be homopolymers orcopolymers.

[0074] The conjugated polymer used can be any of the conjugated polymersdisclosed or referred to in U.S. Pat. No. 5,807,627, PCT/WO90/13148 andPCT/WO92/03490.

[0075] The conjugated polymers disclosed are poly(p-phenylenevinylene)-PPV and copolymers including PPV. Other preferredpolymers are poly(2,5 dialkoxyphenylene vinylene) such aspoly(2-methoxy-5-(2-methoxypentyloxy-1,4-phenylene vinylene),poly(2-methoxypentyloxy)-1,4-phenylenevinylene),poly(2-methoxy-5-(2-dodecyloxy-1,4-phenylenevinylene) and other poly(2,5dialkoxyphenylenevinylenes) with at least one of the alkoxy groups beinga long chain solubilising alkoxy group, poly fluorenes andoligofluorenes, polyphenylenes and oligophenylenes, polyanthracenes andoligo anthracenes, ploythiophenes and oligothiophenes.

[0076] In PPV the phenylene ring may optionally carry one or moresubstituents e.g. each independently selected from alkyl, preferablymethyl, alkoxy, preferably methoxy or ethoxy.

[0077] Any poly(arylenevinylene) including substituted derivativesthereof can be used and the phenylene ring in poly(p-phenylenevinylene)may be replaced by a fused ring system such as anthracene or naphthlyenering and the number of vinylene groups in each polyphenylenevinylenemoeity can be increased e.g. up to 7 or higher.

[0078] The conjugated polymers can be made by the methods disclosed inU.S. Pat. No. 5,807,627, PCT/WO90/13148 and PCT/WO92/03490.

[0079] The hole transmitting material and the light emitting metalcompound can be mixed to form one layer e.g. in an proportion of 5 to95% of the hole transmitting material to 95 to 5% of the light emittingmetal compound.

[0080] Optionally there is a layer of an electron transmitting materialbetween the cathode and the electroluminescent material layer, theelectron transmitting material is a material which will transportelectrons when an electric current is passed through electrontransmitting materials include a metal complex such as a metal quinolatee.g. an aluminium quinolate, lithium quinolate a cyano anthracene suchas 9,10 dicyano anthracene, a polystyrene sulphonate and compounds offormulae shown in FIG. 10. Instead of being a separate layer theelectron transmitting material can be mixed with the electroluminescentmaterial to form one layer e.g. in a proportion of 5 to 95% of theelectron transmitting material to 95 to 5% of the light emitting metalcompound.

[0081] The electroluminescent layer can comprise a mixture of the lightemitting metal compound with the hole transmitting material and electrontransmitting material

[0082] The electroluminescent material can be deposited on the substratedirectly by vacuum evaporation or evaporation from a solution in anorganic solvent. The solvent which is used will depend on the materialbut chlorinated hydrocarbons such as dichloromethane and n-methylpyrrolidone; dimethyl sulphoxide; tetra hydrofuran; dimethylformamideetc. are suitable in many cases.

[0083] Alternatively electroluminescent material can be deposited byspin coating from solution, or by vacuum deposition from the solid statee.g. by sputtering, or any other conventional method can be used.

[0084] Preferably the first electrode is a transparent substrate such asa conductive glass or plastic material which acts as the anode,preferred substrates are conductive glasses such as indium tin oxidecoated glass, but any glass which is conductive or has a transparentconductive layer such as a metal or conductive polymer can be used.

[0085] Conductive polymers and conductive polymer coated glass orplastics materials can also be used as the substrate.

[0086] The second electrode functions as the cathode and can be any lowwork function metal e.g. aluminium, calcium, lithium, silver/magnesiumalloys etc., aluminium is a preferred metal.

[0087] The display of the invention may be monochromatic orpolychromatic. Electroluminescent rare earth chelate compounds are knownwhich will emit a range of colours e.g. red, green, and blue light andwhite light and examples are disclosed in Patent Applications WO98/58037PCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024,PCT/GB99/04028, PCT/GB00/00268 and can be used to form OLEDs emittingthose colours. Thus, a full colour display can be formed by arrangingthree individual backplanes, each emitting a different primarymonochrome colour, on different sides of an optical system, from anotherside of which a combined colour image can be viewed. Alternatively, rareearth chelate electroluminescent compounds emitting different colourscan be fabricated so that adjacent diode pixels in groups of threeneighbouring pixels produce red, green and blue light. In a furtheralternative, field sequential colour filters can be fitted to a whitelight emitting display.

[0088] Either or both electrodes can be formed of silicon and theelectroluminescent material and intervening layers of a holetransporting and electron transporting materials can be formed as pixelson the silicon substrate. Preferably each pixel comprises at least onelayer of a rare earth chelate electroluminescent material and an (atleast semi-) transparent electrode in contact with the organic layer ona side thereof remote from the substrate.

[0089] Preferably, the substrate is of crystalline silicon and thesurface of the substrate may be polished or smoothed to produce a flatsurface prior to the deposition of electrode, or electroluminescentcompound. Alternatively a non-planarised silicon substrate can be coatedwith a layer of conducting polymer to provide a smooth, flat surfaceprior to deposition of further materials.

[0090] In one embodiment, each pixel comprises a metal electrode incontact with the substrate. Depending on the relative work functions ofthe metal and transparent electrodes, either may serve as the anode withthe other constituting the cathode.

[0091] When the silicon substrate is the cathode an indium tin oxidecoated glass can act as the anode and light is emitted through theanode. When the silicon substrate acts as the anode the cathode can beformed of a transparent electrode which has a suitable work function,for example by a indium zinc oxide coated glass in which the indium zincoxide has a low work function. The anode can have a transparent coatingof a metal formed on it to give a suitable work function. These devicesare sometimes referred to as top emitting devices or back emittingdevices.

[0092] The metal electrode may consist of a plurality of metal layers,for example a higher work function metal such as aluminium deposited onthe substrate and a lower work function metal such as calcium depositedon the higher work function metal. In another example, a further layerof conducting polymer lies on top of a stable metal such as aluminium.

[0093] Preferably, the electrode also acts as a mirror behind each pixeland is either deposited on, or sunk into, the planarised surface of thesubstrate. However, there may alternatively be a light absorbing blacklayer adjacent to the substrate.

[0094] In still another embodiment, selective regions of a bottomconducting polymer layer are made non-conducting by exposure to asuitable aqueous solution allowing formation of arrays of conductingpixel pads which serve as the bottom contacts of the pixel electrodes.

[0095] As described in WO00/60669 the brightness of light emitted fromeach pixel is preferably controllable in an analogue manner by adjustingthe voltage or current applied by the matrix circuitry or by inputting adigital signal which is converted to an analogue signal in each pixelcircuit. The substrate preferably also provides data drivers, dataconverters and scan drivers for processing information to address thearray of pixels so as to create images. When an electroluminescentmaterial is used which emits light of a different colour depending onthe applied voltage the colour of each pixel can be controlled by thematrix circuitry.

[0096] In one embodiment, each pixel is controlled by a switchcomprising a voltage controlled element and a variable resistanceelement, both of which are conveniently formed bymetal-oxide-semiconductor field effect transistors (MOSFETs) or by anactive matrix transistor.

[0097] The electroluminescent materials of the present invention cangenerate electromagnetic radiation in the visible and in the infra redand ultra violet region of the spectrum e.g. 2200 nm to 200 nm,depending on the metal and the ligand.

[0098] Wavelengths in the near infra red region of the spectrum (e.g.1100 nm to 2200 nm) are useful in the transmission of signals down opticfibres and the devices of the present invention can be used to transmitdata down such optic fibres.

[0099] The invention is described with reference to the followingExamples.

EXAMPLE 1 Preparation of Al(DBM)₃

[0100] Tris-(1,3-diphenyl-1-1-propanedione) Aluminium (III), Al(DBM)₃was synthesised according to the reaction

[0101] Dibenzoyl methane (2.78 g: 0.012 mole) was dissolved in ethanol(75 ml) by warming the solution. Sodium hydroxide (0.49 g; 0.012 mole)in water (15 ml) was added to the solution. The light yellow colouredsolution was stirred for 15 minutes and a solution of AlCl₃.6H₂O (1.0g:0.004 mole) in water (15 ml) was slowly added, The reaction mixturewas magnetically stirred and heated at 60° C. for 3 hours and allowed tocool to room temperature. The yellow precipitate was filtered off undersuction, washed with water, followed by ethanol and dried under vacuumat 80° C. for 4 hours. The product was further purified by dissolving indiethylether and precipitating with petroleum ether (40-60° C.). Theproduct was filtered off under suction and dried under vacuum for 8hours at 80° C.

[0102] The product was purified by being dissolved indiethylether/petether and allowed to form a precipitate, elementalanalysis of the product showed it had a composition of 77.24% C and4.79% H; the theoretical composition for Al(DBM)₃ is 77.58% C and 4.77%H.

[0103] The purified product was sublimed under vacuum at 10⁻⁵ Torr andchemical analysis showed that no decomposition of Al(DBM)₃ took place sothat it could be used to form electroluminescent devices by vacuumcoating.

[0104] The optical properties were measured by UV/visible absorbancespectra of solution evaporated thin film (SETF) and vacuum evaporated(VETF) Al(DBM)₃, and the results shown in Table 1. TABLE 1 SETF -λ_(max)/nm VETF - λ_(max)/nm Al(DBM)₃ 265, 371 260, 370

[0105] The λ_(max) value of Al(DBM)₃ VET film and SET film are almostsame. Therefore UV/Visible light data also proved that no decompositionof Al(DBM)₃ takes place in evaporation under vacuum.

[0106] Device Fabrication and Characterisation

[0107] A double layer device as illustrated in FIG. 17 was constructed,in the device the ITO coated glass had a resistance of about 10 ohms. AnITO coated glass piece (1×1 cm²) had a portion etched out withconcentrated hydrochloric acid to remove the ITO and was cleaned anddried. The device was fabricated by sequentially forming on the ITO, byvacuum evaporation at 1×10⁻⁵ Torr, a TPD hole transmitting layer and theelectroluminescent layer.

[0108] The photoluminescent and electroluminescent spectra at 12 voltsare shown in FIG. 18. The onset of luminescence was at about 4 voltsshowing as a bright saturated yellow luminescence with colourcoordinates 0.5, 0.49. The luminescence increases with increasingvoltage and the spectrum of FIG. 18 was recorded when luminescence was12.6 cd m⁻² (12 volts, 6.75 mA cm⁻². The luminescence, voltage, currentdensity and luminescence efficiency, voltage, current efficiencycharacterisation of the device is shown in FIGS. 19 and 20. A maximumluminance of about 279 cd m⁻² was observed at a current density of 87 mAcm⁻² and a driving voltage of 23 volts and at this voltage a luminanceof 0.15 cd A⁻¹ and 0.02 lm W⁻¹ was obtained.

[0109] The luminescence, current density, luminescent efficiency and theluminescence, current density, current efficiency characterizations areshown in FIGS. 21 and 22. The maximum luminescence efficiency of 0.05 lmW⁻¹ at 15 volts, current efficiencies of 0.25 cd A⁻¹ (21 mA cm⁻²) and abrightness of 5 cd m⁻² were obtained. The change in CIE colourcoordinates with voltage is shown in Table 2. TABLE 2 V Cd m⁻² x: Y: 9 20.50 0.48 12 12.6 0.50 0.49 15 55 0.49 0.49 17 104 0.49 0.49 19 194 0.480.49 21 249 0.48 0.49 23 279 0.48 0.49

EXAMPLE 2 Preparation of Mg(DBM)₂

[0110] Dibenzoylmethane (10.9 g; 0.049 mole) was dissolved in ethanol(100 ml) by warming the solution. MgCl₂ (5.0 g; 0.025 mole) in water (10ml) was added followed by 2N NaOH solution until the pH was 6-7. Theprecipitate was heated at 60° C. for 2 hours, cooled and filtered offunder suction. The precipitate was washed thoroughly with water,followed by ethanol and diethyl ether. The product dried under vacuumoven at 80° C. for 6 hours and the emission spectra shown in FIG. 23.

EXAMPLE 3 Preparation of Sc(DBM)₃

[0111] Dibenzoylmethane (13.5 g; 0.06 1 mole) was dissolved in ethanol(125 ml) by warming the solution to 60° C. Small amounts of NaOH (10%solution) was first added to the DBM solution. The solution became lightyellow in colour. ScCl₃.H₂O (3.0 g; 0.020 mole) in water(10 ml) wasadded. A light yellow precipitate formed immediately. The NaOH solutionwas further added until the pH of the mixture was between 7-8. Thereaction mixture was stirred and heated at 60° C. for 1 hour, cooled andfiltered off under suction. The precipitate was again taken-up inethanol (150 ml) and refluxed for 1 hour. The product was allowed tocool and filtered off under suction and dried under vacuum at 90° C. forabout 6 hours

EXAMPLE 4 Preparation of Zn(DBM)₂

[0112] Dibenzoylmethane (25.0 g; 0.11 mole) was dissolved in ethanol(200 ml) by warming the solution ZnCl₂ (7.5 g, 0.055 mole) in water (10ml) was added followed by 2N NaOH solution until the pH was 7. The lightyellow precipitate was warmed for 1 hour and cooled to room temperature.The light yellow precipitate was filtered off, washed thoroughly withwater followed by ethanol and dried under vacuum at 80° C. for 10 hours.It exhibited bluish-white fluorescence and the emission spectra shown inFIG. 24.

[0113] The photoluminescence spectra were studied using a 100 mg discand a vacuum evaporated thin film and the results shown in Table 3 TABLE3 PL Material λmax/nm (x, y) η/% Al(DBM)₃ 442,565 (0.34, 0.36) 15 ± 3 Zn(DBM)₂ 500 (0.31, 0.41) 4 ± 1 Mg(DBM)₂ 473 (0.20, 0.28)   1 ± 0.5Sc(DBM)₃ 586 (0.48, 0.48) 35 ± 5 

EXAMPLE 5 Preparation of Aluminium(1,3-Bis-(4-methoxy-phenyl)-propane-1,3 dione)

[0114] The anion of 1,3-bis-(4-methoxy-phenyl)-propane-1,3 dione wasprepared by addition of equimolar amounts of NaOH (3.5 mM in 10 mlwater) to an ethanolic solution of1,3-bis-(4-methoxy-phenyl)-propane-1,3 dione (3.5 mM in 50 ml ethanol)at 60° C. Introduction of aqueous solution of AlCl₃.6H₂0 (1. mM in 15 mlwater) to the anion mixture afforded the desired complex as a paleyellow powder after stirring for 3 hours at 60° C. The compound wassuction filtered and thoroughly washed with water. Then it was followedby a small amount of ethanol. It was dried at 75° C. for 8 hours mp 310°C. Yield: 75%. Elemental analysis of Al complex found C, 69.80; H, 5.26%Calc. for Al(C₅₁H₄₅O₁₂): C, 69.86; H, 5.13%

[0115] An electroluminescent was fabricated as in Example 1 and thecolour coordinates of the emitted light were x=0.21, y=0.22 and λ_(max)(emission) was 460 nm.

EXAMPLE 6 Preparation of Aluminium (1-(4-methoxy-phenyl)-propane-1,3dione)

[0116] The anion of 1-(4-methoxy-phenyl)-3-phenyl-propane-1,3 dione wasprepared by the addition of equimolar amounts of NaOH (3.9 mM in 15 mlwater) to an ethanolic solution ofli-(4-methoxy-phenyl)-3-phenyl-propane-1,3 dione (3.9 mM in 50 mlethanol) at 60° C. The introduction of aqueous solution of AlCl₃.6H₂O(1.3 mM in 20 ml water) to the anion mixture afforded the desiredcomplex as a pale yellow powder after stirring for 3 hours at 60° C. Thecompound was suction filtered and thoroughly washed with water followedby a small amount of ethanol. It was dried at 75° C. for 8 hours.

[0117] An electroluminescent was fabricated as in Example 1 and thecolour coordinates of the emitted light were x=0.36, y=0.41 and λ_(max)(emission) was 550 nm.

EXAMPLE 7 Preparation of Scandium(1,3-Bis-(4-methoxy-phenyl)-propane-1,3 dione)

[0118] The anion of 1,3-bis-(4-methoxy-phenyl)-propane-1,3 dione wasprepared by the addition of equimolar amounts of NaOH (3.5 mM in 10 mlwater ) to an ethanolic solution of1,3-bis-(4-methoxy-phenyl)-propane-1,3 dione (3.5 mM in 50 ml ethanol)at 60° C. The introduction of an aqueous solution of ScCl₃.6H₂0 (1.1 mMin 15 ml water) to the anion mixture afforded the desired complex as apale yellow powder—after stirring for 3 hours at 60° C. The compound wassuction filtered and thoroughly washed with water followed by a smallamount of ethanol. It was dried at 75° C. for 8 hours. mp 335° C. Yield65%. Elemental analysis of Sc complex found C, 67.91; H, 5.21% Calc. forSc(C₅₁H₄₅O₁₂): C, 68.38; H, 5.02%

[0119] An electroluminescent was fabricated as in Example 1 and thecolour coordinates of the emitted light were x=0.25, y=0.3 and λ_(max)(emission) was 465 nm.

EXAMPLE 8 Preparation of Scandium (1-(4-methoxy-phenyl)-propane-1,3dione)

[0120] The anion of 1-(4-methoxy-phenyl)-3-phenyl-propane-1,3 dione wasprepared by addition of equimolar amounts of NaOH (3.9 mM in 15 mlwater) to an ethanolic solution of1-(4-methoxy-phenyl)-3-phenyl-propane-1,3 dione (3.9 mM in 50 mlethanol) at 60° C. Introduction of aqueous solution of ScCl₃.6H₂0 (1.3mM in 20 ml water) to the anion mixture afforded the desired complex asa pale yellow powder after stirring for 3 hours at 60° C. The compoundwas suction filtered and thoroughly washed with water followed by asmall amount of ethanol. It was dried at 75° C. for 8 hours.

[0121] An electroluminescent was fabricated as in Example 1 and thecolour coordinates of the emitted light were x=0.36, y=0.41 and λ_(max)(emission) was 550 nm.

EXAMPLE 9 Preparation of Scandium (1,3-di-p-tolyl-propane-],3 dione)

[0122] The anion of 1,3-di-p-tolyl-propane-],3 dione was prepared byadding of equimolar amounts of NaOH (2.9 mM in 10 ml water) to anethanolic solution of 1,3-di-tolyl-propane-1,3 dione (2.9 mM in 50 mlethanol) at 60° C. Introduction of aqueous solution of AlCl₃.6H₂0 (0.9mM in 15 ml water) to the anion mixture afforded the desired complex asa pale yellow powder after stirring for 3 hours at 60° C. The compoundwas suction filtered and thoroughly washed with water followed by asmall amount of ethanol. It was dried at 75° C. for 8 hours.

[0123] An electroluminescent was fabricated as in Example 1 and thecolour coordinates of the emitted light were x=0.17, y=0.23 and λ_(max)(emission) was 465 nm.

EXAMPLE 10 Preparation of Al(L_(α))₂(L₁)

[0124] (L_(α)) was

[0125] The mixed complex was made by the procedure of example 5 and anelectroluminescent device was fabricated as in Example 1 and theemission spectrum is shown in FIG. 25.

1. An electroluminescent device comprising (i) a first electrode (ii) anelectroluminescent layer comprising a layer of a light emitting metalcompound selected from organic complexes of formula (M)_(n+m) (Lα)_(n)(L₁)_(m), where M is a non rare earth metal, n+m is the valency state ofM and m can be 0, Lα is as specified in the specification and L₁ is acharged organic ligand and (iii) a second electrode.
 2. Anelectroluminescent device as claimed in claim 1 in which the metal M islithium, sodium, potassium, rubidium, caesium, beryllium, magnesium,calcium, strontium, barium, copper, silver, gold, zinc, cadmium, boron,aluminium, gallium, indium, germanium, tin, antimony, lead, and metalsof the first, second and third groups of transition metals e.g.manganese, iron, ruthenium, osmium, cobalt, nickel, palladium, platinum,cadmium, chromium. titanium, vanadium, zirconium, tantulum, molybdenum,rhodium, iridium, titanium, niobium, scandium, yttrium
 3. Anelectroluminescent device as claimed in claim 1 or 2 in which the lightemitting metal compound has the formula (M)(Lα)_(n) where M is the metaland Lα is an organic ligand as specified in the specification.
 4. Anelectroluminescent device as claimed in claim 3 in which Lα has theformula (I) to (XVII) herein.
 5. An electroluminescent device as claimedin claim 1 in which the light emitting metal compound has the formula

where R₄ is an alky group and R₃ is hydrogen, an alkyl group or R₄O. 6.An electroluminescent device as claimed in claim 5 where R₄ and R₃ aremethyl groups.
 7. An electroluminescent device as claimed in any one ofclaims 1 to 6 which the light emitting metal compound has the formula

where Lp is a ligand of formula (XVIII) to (XXV) herein or of formula ofFIGS. 1 to 8 of the accompanying drawings.
 8. An electroluminescentdevice as claimed in any one of claims 1 to 7 in which there is a layerof a hole transmitting material between the first electrode and theelectroluminescent layer.
 9. An electroluminescent device as claimed inany one of claims 1 to 8 in which a hole transmitting material and thelight emitting metal compound are mixed to form one layer.
 10. Anelectroluminescent device as claimed in claim 8 or 9 in which the holetransmitting material is an aromatic amine complex
 11. Anelectroluminescent device as claimed in claim 8 or 9 in which the holetransmitting material is a film of a polymer selected frompoly(vinylcarbazole),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD),polyaniline, substituted polyanilines, polythiophenes, substitutedpolythiophenes, polysilanes and substituted polysilanes.
 12. Anelectroluminescent device as claimed in claim 8 or 9 in which the holetransmitting material is a film of a compound of formula (II) or (III)herein or as in FIGS. 11, 12, 13, or 14 of the drawings.
 13. Anelectroluminescent device as claimed in any one of claims 1 to 12 inwhich there is a layer of an electron transmitting material between thecathode and the electroluminescent material layer.
 14. Anelectroluminescent device as claimed in any one of claims 1 to 12 inwhich an electron transmitting material and the light emitting metalcompound are mixed to form one layer.
 15. An electroluminescent deviceas claimed in claim 13 or 14 in which the electron transmitting materialis a metal quinolate.
 16. An electroluminescent device as claimed inclaim 15 in which the metal quinolate is an aluminium quinolate orlithium quinolate
 17. An electroluminescent device as claimed in claim13 or 14 in which the electron transmitting material is a cyanoanthracene such as 9,10 dicyano anthracene, a polystyrene sulphonate ora compound of formulae shown in FIG.
 10. 18. An electroluminescentdevice as claimed in any one of claims 13 to 17 in which a holetransmitting material and an electron transmitting material and thelight emitting metal compound are mixed to form one layer.
 19. Anelectroluminescent device as claimed in any one of the preceding claimsin which the second electrode is selected from aluminium, calcium,lithium, silver/magnesium alloys
 20. An electroluminescent device asclaimed in any one of the preceding claims in which there is a lithiumfluoride layer formed on the second electrode.
 21. An electroluminescentdevice as claimed in any one of the preceding claims which emits lightwith a wavelength in the range of 400 nm to 2200 nm.
 22. Anelectroluminescent device as claimed in claim 21 which emits light inthe in the near infrared region of the spectrum.
 23. Anelectroluminescent device as claimed in any one of the preceding claimsin which L₁ has the formula


25. A compound of the formula

where R₄ is an alky group and R₃ is hydrogen, an alkyl group or R₄O. 26.A compound as claimed in claim 25 where R₃ and R₄ are methyl groups.